Overzealous change detection

[Rich-Harris]

#2694 introduced a new bug — Svelte is now over-eager when marking values as having changed. The bug can be seen in this demo — it's not present in 3.2.0.

Workaround in the meantime appears to be to manually reorder reactive declarations.

[benjamingr]

I'm definitely running into this :]

[benjamingr]

Wouldn't it be better to invalidate the property and not the object when it is statically safe to do so?

That is, I was surprised o.a += 1 invaldiates o and not o.a like in vue or mobx. I realize it's not possible to do for the general case but for property access in assignment I think it's relatively safe.

[Conduitry]

Looks to be probably the same as #2748 and #2873, although as those issues show, this is also a problem when there aren't multiple reactive declarations. I don't know which one we want to consider the main issue for this, but I had done a little analysis in #2873.

[Panya]

It was fixed in 3.4.4 and above.

[Conduitry]

This issue was being masked in 3.4.4 and above by #2865, but it looks like it would be actually fixed by #3533.

[Conduitry]

Fixed in 3.10.1.

[benjamingr]

@Conduitry sorry for the (probabably dumb) question - but how was it fixed in 3.10.1? Can you link to a PR or issue?

(asking for purely intellectual purposes to learn what svelte ended up doing)

[Conduitry]

I mentioned it in my previous comment - it was fixed via #3533.